Scientists have created hundreds of mutant fish with "six-pack abs" and bulging "shoulders" by beefing them up with new genes.

While the fish aren't going to win any beauty contests, the genetically engineered rainbow trout could hold some appeal at market, because they each provide 15 to 20 percent more flesh than standard tout, researchers say.

Developed with fish farming in mind, the genetically modified trout is the result of ten years of experimentation by a team led by Terry Bradley of the University of Rhode Island's Department ofFisheries, Animal, and Veterinary Sciences.

The team injected 20,000 rainbow trout eggs with different types of DNA from other species, making them transgenic. The added DNA was intended to suppress a protein called myostatin, and it apparently worked in about 300 of the eggs, turning them into the muscle-bound superfish.

The transgenic trout incorporate genes modeled on myostatin-inhibiting proteins found in powerfully built Belgian blue cattle, a beef breed noted for its "double muscled" appearance.

In mammals, including humans, mysostatin is known to keep muscle growth in check—controlling myostatin is touted as a potential way to reverse muscle-wasting diseases in humans.

"Under certain conditions the transgenic fish do better than the wild types, but under other conditions we see the opposite," he added.

"If they have a lot of food, transgenic fish can use that food to a greater extent, but if you have predators nearby they also seem to be more susceptible to predation," Sundström said.

He doubts, however, whether this latest transgenic trout would find enough food in the wild to support its body builder physique—or that the bulky fish would be able to maneuver swiftly enough to avoid being eaten.

But if the fish did survive in the wild—for instance, if juveniles are able to "grow too big for birds to feed on them"—they could overturn their ecosystems, Sundström said. For one thing, he said, the six-pack trout's greater size could allow them to outcompete their unmodified cousins, leaving them with little food and an imperiled future.